The present invention relates to a method, a recording support and a device to calibrate fuel injection.
The Applicant knows a method to calibrate the fuel injection in at least one combustion chamber of a Diesel engine. Each combustion chamber has a piston that moves along a piston stroke between a top dead center and a bottom dead center.
For example, it is known from DE 196 12 179 to measure the combustion noise using knock sensors and to compare the measured combustion noise to a predetermined threshold SW.
By “combustion noise” we mean the noise produced by the fuel when it is injected in the combustion chamber and the noise produced by the explosion of the injected fuel in the combustion chamber. This combustion noise is not a mechanical noise produced by impacts or chocks on mechanical parts of the Diesel engine. The combustion noise is the vibration of the engine structure caused by the fuel injection and the fuel explosion.
For memory, it is reminded that the time at which the fuel explosion takes place in a combustion chamber of a Diesel engine is not known accurately because such explosion is not triggered by a spark like in other combustion engines.
In DE 196 12 179, the time Tc at which the measured combustion noise exceeds threshold SW is considered as being the time when the fuel explosion begins in the combustion chamber. This information on time Tc allows to adjust the fuel injection in this particular combustion chamber.
However, this method is not very reliable. In fact, time Tc varies from one engine cycle to the other even if every Diesel engine parameters are maintained constants from one cycle to the other. The engine cycle is defined as being the time range or the piston position range over which only one fuel explosion takes place in each of the combustion chambers of the engine.
Time Tc is not a very accurate representation of the actual time at which the fuel explosion begins. Thus, any fuel injection adjustment based on this time Tc is not very reliable.
Accordingly, it is desirable to provide a more reliable method to calibrate the fuel injection in at least one combustion chamber of a Diesel engine.
The invention provides, according to an aspect thereof, a fuel injection calibration method comprising for at least one combustion chamber:
a) recording the combustion noise power or amplitude in the combustion chamber over a piston position range [γ1i;γ2i] where γ1i, is a piston position where the fuel is injected into the combustion chamber and γ2i is a piston position where the explosion of the injected fuel has already begun,
b) at the same time, recording the piston position during the same piston position range [γ1i;γ2i],
c) determining from the preceding recordings for which piston position Kmin-i relative to the top dead center of the combustion chamber, the measured combustion noise power passes through a minimum Pmin-i when the piston moves from position γ1i to position γ2i,
d) adjusting (94) the fuel injection according to the determined piston position Kmin-i.
As a result, the piston position Kmin-i, is more accurately correlated with the piston position where the fuel explosion takes place than the position where the combustion noise power exceeds a predetermined threshold. Thus, using piston position Kmin-i to adjust the fuel injection increases the reliability of the method.
The embodiments of the above method may comprise one or several of the following features:                the piston position Kmin-i is determined for each combustion chamber and adjusting the fuel injection comprises adjusting the fuel injection timing in each combustion chamber so that the piston positions Kmin-l in each combustion chamber are closer to each other,        the method further comprises:                    computing an average position Kmin from the positions Kmin-i determined for each combustion chamber, and            adjusting the fuel injection timing in each combustion chamber so that the piston positions Kmin-i in each combustion chamber are equal to this average position Kmin,                        the combustion noise power or amplitude is only recorded for frequencies ranging between 7.5 kHz and 8.5 kHz,        for at least one combustion chamber:                    the fuel injection adjustment is performed for different engine speed and engine torque and corresponding fuel injection correction factors are recorded in a memory, and            for a given engine speed or an engine torque, the correction factors to be applied to adjust the fuel injection are recovered from said previously recorded correction factors according to the present engine speed and the present engine torque without proceeding to a new determination of the piston position Kmin-i, and                        the piston position range [γ1i;γ2i] is shorter than the piston position range extending from the bottom dead center to the top dead center.        
The above embodiments of the method present the following advantages:                adjusting the fuel injection timing so that positions Kmin-i are equal or nearly equal in every combustion chamber ensures a smoother rotation of the crankshaft and reduces engine vibrations,        adjusting the fuel injection timing so that positions Kmin-i in every combustion chamber are equal to the average position Kmin further reduces the engine vibrations,        only using noise frequencies ranging between 7.5 kHz and 8.5 kHz increases the reliability of the method because this frequency range is less disrupted by mechanical noises,        recording the fuel injection correction factors for specific engine speeds and torques simplifies the fuel injection adjustment.        
The invention also relates to an information recording support comprising instructions to execute the above method when the instructions are executed by an electronic calculator.
The invention also relates to a device to calibrate the fuel injection in at least one combustion chamber of a Diesel engine, the combustion chamber having a piston that moves along a piston stroke between a top dead center and a bottom dead center, the device comprising:                at least one knock sensor fixedly registered to the Diesel engine to measure the combustion noise power or amplitude in the combustion chamber,        at least one piston position sensor able to sense the piston position along the piston stroke,        an electronic calculator able to:                    record the measured combustion noise power or amplitude in the combustion chamber over a piston position range [γ1i;γ2i], where γ2i is a piston position where the fuel is injected into the combustion chamber and γ2i is a piston position where the explosion of the injected fuel has already begun,            at the same time, record the piston position over the same piston position range,            determine from the preceding recordings for which piston position Kmin-i relative to the top dead center of this combustion chamber the measured combustion noise power passes through a minimum Pmin-i when the piston moves from position γ1i to position γ2i, and            adjust the fuel injection according to the determined piston position.                        
These and other aspects of the invention will be apparent from the following description, drawings and claims.
In these drawings, the same reference numbers are used to designate the same elements.
In the following description, well-known functions or constructions by a person of ordinary skill in the art are not described in details.